This invention relates generally to polymer displays which have light emitting layers that are semiconductive polymers.
Polymer displays use layers of light emitting polymers. Unlike liquid crystal devices, the polymer displays actually emit light which makes them advantageous for many applications.
Generally, polymer displays use at least one semiconductive conjugated polymer sandwiched between a pair of contact layers. The contact layers produce an electric field which injects charge carriers into the polymer layer. When the charge carriers combine in the polymer layer, the charge carriers decay and emit radiation in the visible range.
One semiconductive conjugated polymer that may be used in polymer displays in poly(p-phenylenevinylene) (PPV) which emits green light. Another polymer which emits red-orange light is poly(methylethylhexyloxy-p-phenylenevinylene) (MEH-PPV). Other polymers of this class are also capable of emitting blue light. In addition, nitrile substitute conjugated polymers may be used in forming polymer displays. Still other polymers are discussed in U.S. Pat. No. 5,821,690 to Martens et al. and assigned to Cambridge Display Technology Limited.
Polymer displays are limited by the spectral characteristics of the specific polymers chosen. Currently available polymers for use in polymer displays have a rather wide potential color gamut. The most efficient emitters, both electrically and from a human sensitivity perspective, do not have a wide color gamut but instead are rather "pastel". There exist deep blue and deep red emitters, but because of the responsivity roll-off of the eye in the deep red and deep blue regions, these colors are not efficiently used.
Cambridge Display Technology Ltd. has proposed using more than the three standard red, green and blue colors in polymer displays, referred to herein as extended color polymer displays. For colors that are close to white or pastel, the more efficient emitters would be used. When these emitters are out of gamut, which occurs for deep red or deep blue for example, the other red and/or blue emitters are operated. If three out of the five available colors are used at any time one must determine which tricolor space to use in any given situation.
Thus, there is a continuing need for a way to implement extended color polymer displays.